Summary: We have identified and cloned a novel mammalian putative protein kinase which which we have named small serine-threonine protein kinase (SSTK). The cDNA for the human and murine orthologs have been deposited into GenBank under accession numbers AF329483 and AF329484, respectively.The gene was found in the human genome on chromosome 19 between two unidentified genes oriented in the opposite direction. Murine ortholog of the sstk gene was found in the mouse genome draft. The sstk gene from both species contains a single 822-bp open frame that encodes a 273 amino acid peptide. Sequences of human and murine sstk genes are highly homologous (90% identity in DNA coding sequences and 97% identity in amino acid sequence). SSTK protein product almost entirely consists of a putative serine-threonine protein kinase domain (amino acids 12-267), that has all essential conserved features of a protein kinase, including the catalytic residue (Asp135) and the ATP-binding site (Lys41). The search in GenBank revealed the highest, albeit limited, homology of SSTK to Mus musculus testis-specific serine kinases tssk-3 (47% identity), tsk-1 and tssk-2 (45% identity), whereas no significant identity was found in databases of lower organisms. It is our goal to understand the biological role and function of mammalian SSTK. The following studies are currently underway: 1. yeast two-hybrid studies to identify interacting proteins and/or additional subunits 2. experimental confirmation that SSTK is a protein kinase 3. determination of tissue and cellular expression pattern for SSTK 4. elucidation of SSTK substrate specificity and mechanism of enzymatic activation 5. production and characterization of anti-SSTK antibodies 6. generation of an SSTK knockout mouse